This invention relates to electronic throttle controlled engines and more particularly to systems and method for intervening in such throttle control in the event of an apparent fault in estimates of engine operating parameters used to control such throttle.
As is known in the art, a torque monitor function is used for engines equipped with electronic throttle control. This function achieves a high level of safety by checking the desired engine torque, (i.e., driver demanded torque from, for example, a sensing of driver accelerator pedal position) with two independent measures of torque, for example, a throttle based (e.g., throttle position) estimate and an air-meter (i.e., Mass Air Flow, MAF) based method. If the air-meter based method calculates a torque that exceeds the driver demanded torque, the torque monitor function will intervene by one of several methods including shutting off fuel to cylinders.
The inventors have recognized that if a real failure has occurred, say due to a stuck open throttle, then this intervention is appropriate. However, if the intervention was due to other factors, like an air-meter which reads too high due to dirt, or a whole host of other reasons, then the intervention is obnoxious to the driver, and shutting off fuel to cylinders is probably not an appropriate control reaction to measurement errors. In such case, intervention should be prevented.
The general philosophy of intervention prevention is that if the vehicle behavior can be modified in a subtle manner not likely to be noticed by the driver in order to prevent monitor intervention (e.g., shutting off fuel to cylinders), then such modification is a more preferable choice. Even if the driver notices the control changes as a result of intervention modification by vehicle behavior modification in such a subtle manner, such intervention modification may still be a better control choice than an intervention which shuts off fuel to cylinders. So in the end intervention should be limited to real failures, as opposed to momentary misalignment of various calculations due to a number of inconsequential factors.
One known torque monitoring algorithm compares torque demand (i.e., driver-demanded torque computed primarily from acceleration pedal position), with two independent torque estimates (e.g., one estimated from throttle position and one estimated from mass airflow (MAF) to the intake manifold). If the maximum of the two actual torque estimates exceeds the driver-demanded torque, the monitoring algorithm logic intervenes in engine torque production (e.g., shuts off fuel to cylinders) and lights a service (wrench) light.
In accordance with the invention, in order to prevent, or minimize, unnecessary intervention, an adjustment is made to the driver-demanded torque. For example, driver-demanded torque is reduced by a factor based on the ratio of the two actual torque estimates thereby minimizing the cases where the monitor will intervene by, for example, shutting off fuel to cylinders.
In one embodiment, a method is provided for controlling intervention of an internal combustion engine having an electronically controlled throttle. The method includes comparing at least two independent estimates of torque with a commanded torque demand on the engine. If the maximum of the two independent estimates of torque exceeds the commanded torque demand, torque demand on the engine is potentially intervened. If the load as estimated from an airmeter is greater than the load estimated from the throttle, then the demand is reduced to prevent said potential intervention.
In one embodiment, if such comparison indicates the maximum of the two torque estimates exceeds the torque demand, potentially intervening in engine torque production, and, in order to prevent, or minimize, unnecessary engine torque production intervention, reducing a torque demand signal to the throttle by a factor, such factor being a function of airflow meter demand divided by throttle demand.
In accordance with another feature of the invention, a method for controlling intervention of an internal combustion engine is provided. The engine includes an electronically controlled throttle disposed in the airflow to an intake manifold of the engine and an airflow meter disposed in such airflow to the intake manifold of the engine. The engine has a torque demand input to the engine through an operator pedal. The torque demand increases as such pedal position increases and decreases as such pedal position decreases, such torque demand producing a signal fed to the electronically controlled throttle. The method includes comparing, measured throttle load with measured airflow load. If the measured airflow load is greater than the measured throttle load, calculating a factor tr_intprv_ml, where tr_intprv_ml is equal to F1xe2x80x2+(1xe2x88x92F1xe2x80x2) P, where: F1xe2x80x2 is a function of measured throttle load divided by measured airflow load and P=0 if pedal position is relatively low, 1 if pedal position exceed a predetermined relatively high pedal position, or a proportional intermediate value between 0 and 1 if the pedal position is between the relatively low and relatively high pedal positions and applying such calculated factor to the signal fed to the electronically controlled throttle. If the measured airflow load is less than the measured throttle load having the factor tr_intprv_ml equal to a value of 1.
With such method, if the air-meter reads higher than the throttle based estimate of air and torque, then the method simply closes the throttle until the air-meter is satisfied. It is judged that most drivers will not notice that they are getting slightly less torque at a given pedal position, and even if they notice will prefer this control action to an intervention. Further, if the driver still wishes higher torque than produced by the driver-demanded torque which has been reduced by the applied factor, the driver will merely demand more torque by increase accelerator pedal position. More particularly, at high pedal angles (i.e., the driver depresses the accelerator pedal to, or near, its maximum thereby demanding maximum torque), the method disables intervention completely. That is, if the driver is demanding close to maximum torque, then it doesn""t make sense to monitor power greater than demand; the driver wants all the torque available. This override of intervention prevention is achieved in a smooth and continuous manner with the logic by blending the effect out over a range of pedal angle. The same blending is done to disable the monitor itself, using the same ramp versus pedal. However, if the throttle is stuck this method will not be able to prevent the intervention, which is appropriate.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.